code: def is_all(arg):
      """Return true if the argument is a special symbol for all nodes or edges."""
      return isinstance(arg, str) and arg == ALL
  
file_path: dgl/python/dgl/base.py
imports: from __future__ import absolute_import
  import warnings
  from ._ffi.base import DGLError
  from ._ffi.function import _init_internal_api
label_desc: Use image node_id 2 for calling a global function with example usage: is_all(arg) and returns: unknown